This application claims the priority benefit of Japanese application serial no. 2000-071619, filed Mar. 15, 2000.
1. Field of the Invention
This invention relates in general to a rotary compressor using a freon without containing chlorine ions, and using polyol ester as a lubricant or plyvinyl ether as a base oil for preventing abnormal abrasion, and more specifically relates to a structure of a vane and a roller of a highly reliable rotary compressor.
2. Description of Related Art
Traditionally, the freon used for most compressors within refrigerators, showcases, vending machines, or air-conditioners for family and businesses are dichrolrodifluoromethane (R12) and monochrolrodifluoromethane (R22). The traditional freons R12 and R22 easily damage the ozone layer when they are released into the atmosphere. Consequently, use of the traditional freon is restricted. Damage to the ozone layer of the atmosphere is due to chlorine components in the freon. Therefore, a natural freon without chlorine ions, such as HFC freon (for example, R32, R125, and R134a), phytane type freon (for example, propane and butane etc.), carbonic acid gas and ammonia etc, is considered to replace the traditional freon.
FIG. 1 is a cross-sectional view of a rotary compressor with two cylinders, FIG. 2 is a diagram for showing a structural correlation among a roller, a vane and a cylinder, FIG. 3 is a diagram for showing a vane structure. As shown in FIG. 1, the rotary compressor 1 comprises a sealed container 10 with an electromotor and a compressor both installed within the sealed container 10. The electromotor 20 includes a stator 22 and a rotor 24, both of which are fixed on inner walls of the sealed container 10. A rotary shaft 25 passing through the center of the rotor 24 is freely rotated to support two plates 33, 34 that are used to seal the openings of the cylinders 31, 32. A crank 26 is eccentrically connected to the rotary shaft 25. The cylinders 31, 32 are mounted between the two plates 33, 34. The axes of the two cylinders 31, 32 are aligned with the axis of the rotary shaft 25. Hereinafter, only the cylinder 32 is described for simplification. At the sidewall 32b of the cylinder 32, a freon inlet 23 and a freon outlet 35 are formed respectively.
Within the cylinder 32, an annular roller 38 is mounted. The inner circumference 38b of the roller 38 is in contact with the outer circumference 26a of the crank 26, and the outer circumference 38a of the roller 38 is in contact with the inner circumference 32b of the cylinder 32. A vane 40 is mounted on the cylinder 32 and capable of sliding freely. The front end 40a of the vane 40 is elastically in contact with the outer circumference 38a of the roller 38. The front end 40a of the vane 40 and the roller 38 are securely sealed by introducing a compressed freon from the vane 40. A compressing room 50 is then encompassed by the roller 38, the cylinder 32, and the plate 34 for sealing the cylinder 32.
When the rotary shaft 25 rotates counterclockwise with respect to FIG. 2, the roller 38 rotates eccentrically within the cylinder 32. Therefore, freon gas is introduced into the compressing room 50 from the inlet 23, compressed and then exhausted from the outlet 35. During the cycle, a compressing stress Fv is generated at the contact portion of the vane 40 and the roller 38.
According to the traditional structure, the contact surface (the front end) 40a of the vane 40 in contact with the roller 38 is an arc shape with a radius of curvature Rv. The radius of curvature Rv is substantially equal to the width of the vane 40, and about {fraction (1/10)} to ⅓ of the radius of the roller 38. The roller 38 is made of materials such as cast iron or cast iron alloy, and is formed by a quenching process. The vane 40 is made of materials such as stainless steel or tool steel, and can be further coated by nitridation. In general, the vane 40 is characterized by high hardness and malleability.
FIG. 4 shows the contact status between the roller 38 and the vane, however a cylindrical tube with different radius of curvature can be used. As shown in FIG. 4, due to the compressing stress Fv of the vane 40, it is a surface contact, rather than a point contact or a line contact, between the vane 40 and the roller 38 when they squeeze each other. The length of an elastic contact surface between the vane 40 and the roller 38 can be calculated by the following formula:   d  =      4    ⁢                            (                                                    1                -                                  v                  1                  2                                                            π                ⁢                                  xe2x80x83                                ⁢                E1                                      +                                          1                -                                  v                  2                  2                                                            π                ⁢                                  xe2x80x83                                ⁢                E2                                              )                ·        Fv        ·                  ρ          L                    
wherein E1 and E2 are longitudinal elastic coefficients (kg/cm2) for the vane 40 and the roller 38 respectively, xcexd1 and xcexd2 are Poisson""s ratios for the vane 40 and the roller 38 respectively, L is the height (cm) of the vane 40, Fv is the compressing stress, xcfx81 is a effective radius. At the contact portion, a Hertz stress Pmax (kgfcm2) is exerted and calculated by the following formula:
Pmax=4/xcfx80xc2x7Fv/L/dxe2x80x83xe2x80x83(9)
As the structure described above, in order to increase the durability of the vane a surface process such as a nitridation process or a CrN ion coating film is performed on the vane of the rotary compressor using a freon without containing chlorine ions and using a polyol ester lubricant or plyvinyl ether as a base oil. However, the durability for nitridation is easily degraded and the CrN ion film is easily stripped. Furthermore, the nitridation process or the CrN ion coating film costs high and therefore the manufacturing cost increases.
According to the foregoing description, an object of this invention is to provide a high reliable rotary compressor using a freon without containing chlorine ions, and using a polyol ester as a lubricant or plyvinyl ether as a base oil for preventing abnormal abrasion between the vane and the roller.
According to the present invention, it changes the conventional design that the radius of curvature of the contact surface of the vane and the roller is substantially equal to the width of the vane. To maintain the contact surface of the vane and the roller within an acceptable range, by increasing the radius of curvature of the contact surface to be larger than the width of the vane, the Hertz stress is therefore decreased. In addition, the sliding distance increases for diverging the stress such that the temperature at the sliding contact portion between the vane and the roller can be reduced. Accordingly, a coating process with a high cost is not necessary for the surface of the vane. Namely, even though a low cost nitridation (NV nitridation, sulphonyl nitridation or radical nitridation) is used, it can sufficiently reduce the abrasion between the contact area of the roller and the vane, and further prevent abnormal abrasion.
According to the objects mentioned above, the present invention provides a rotary compressor coupled to a freon loop. The freon loop is connected to the rotary compressor, a condenser, an expansion device and an evaporator. The rotary compressor uses a freon without containing chlorine ions and uses a polyol ester as a lubricant or polyvinyl ether as a base oil for the lubricant. The rotary compressor comprises at least a cylinder, a rotary shaft, a roller and a vane. The cylinder has a freon inlet and a freon outlet. The rotary shaft has a crank installed on an axis of the cylinder. The roller is installed between the crank and the cylinder, and capable of eccentrically rotating. The vane is capable of reciprocating within a groove formed in the cylinder, and sliding contact with an outer circumference of the roller. A sliding contact portion is formed between the vane and the roller, having a radius of curvature Rv satisfying the following formula:
T less than Rv less than Rrxe2x80x83xe2x80x83(1)
wherein T is the thickness of the vane and Rr is the radius of curvature of the outer circumference of the roller sliding contact with the vane.
As mentioned, a distance between a rotation center (O1) of the rotary shaft and a center (O2) of the roller is defined as an eccentricity (E). An angle xcex1 is formed between a first line (L1) and a second line (L2), in which the first line (L1) connects the center (O2) of the roller and a center (O3) of the radius of curvature Rv of the vane, and the second line (L2) connects the center (O3) of the radius of curvature Rv of the vane and the rotation center (O1) of the rotary shaft. A sliding distance connects a first intersection of the first line (L1) with the outer circumference of the roller and a second intersection of the second line (L2) with the outer circumference of the roller. The thickness T, the radii of curvature Rv, Rr, the eccentricity E, the angle xcex1, and the sliding distance (ev) satisfy the following formulae for maintaining a sliding contact surface located at the sliding contact portion between the vane and the roller:
T greater than 2xc2x7Rvxc2x7E/(Rv+Rr)xe2x80x83xe2x80x83(2)
sin xcex1=E/(Rv+Rr)xe2x80x83xe2x80x83(3)
ev=Rvxc2x7E/(Rv+Rr)xe2x80x83xe2x80x83(4)
In addition, the thickness T, the radii of curvature Rv, Rr, the eccentricity E, the angle xcex1, and the sliding distance (ev) satisfy a formula:
T greater than [2xc2x7Rvxc2x7E/(Rv+Rr)]+dxe2x80x83xe2x80x83(8)
for maintaining the sliding contact surface located at the sliding contact portion between the vane and the roller when the rotary compressor is operated with a large loading, in which L is the height of the vane, E1, E2 are longitudinal elastic coefficients, xcexd1 and xcexd2 are Poison""s ratios for the vane and the roller, xcex94P is a designed pressure, is an effective radius, is a stress from the vane, d is a distance of an elastic contact surface, wherein xcfx81, xcex94P, Fv and d are calculated by following formulae:                               1          ρ                =                              1            Rv                    +                      1            Rr                                              (        5        )            xe2x80x83Fv=Txc2x7Lxc2x7xcex94Pxe2x80x83xe2x80x83(6)
                    d        =                  4          ⁢                                                    (                                                                            1                      -                                              v                        1                        2                                                                                    π                      ⁢                                              xe2x80x83                                            ⁢                      E1                                                        +                                                            1                      -                                              v                        2                        2                                                                                    π                      ⁢                                              xe2x80x83                                            ⁢                      E2                                                                      )                            ·              Fv              ·                              ρ                L                                                                        (        7        )            
When the rotary compressor is operated with a large loading, the designed pressure xcex94P is 2.98 Mpa for using an HFC407C freon, 4.14 MPa for using an HFC410A freon, 3.10 MPa for using an HFC404A freon, 1.80 MPa for using an HFC134a freon.
Furthermore, the vane mentioned above is composed of an iron material having a longitudinal elastic coefficient between 1.96xc3x97105xcx9c2.45xc3x97105 N/mm2, and the roller sliding contact with the vane is composed of an iron material having a longitudinal elastic coefficient between 9.81xc3x97104 and 1.47xc3x97105 N/mm2. Preferably, the stokes of the base oil is between 20 and 80 mm2/s at a temperature of about 40xc2x0 C.
The geometry of the vane and the roller above can be designed where a top surface of the vane can be further coated with a compound layer containing an iron-nitrogen (Fexe2x80x94N) base, and a diffusion layer with an iron-nitrogen (Fexe2x80x94N) base formed under the compound layer by nitridation. The top surface of the vane can be alternatively only coated with a compound layer containing an iron-nitrogen (Fexe2x80x94N) base. The top surface of the vane can also be further coated with a compound layer containing an iron-sulfur (Fexe2x80x94S) base, and a diffusion layer with an iron-nitrogen (Fexe2x80x94N) base formed under the compound layer by nitridation.
Furthermore, the top surface of the vane can be coated with a compound layer containing an iron-nitrogen (Fexe2x80x94N) base, and a diffusion layer containing an iron-nitrogen (Fexe2x80x94N) base formed under the compound layer by nitridation, and the compound layer with an iron-nitrogen (Fexe2x80x94N) base coated on at least one side surface of the vane is removed. Alternatively, the top surface of the vane can be further coated with a compound layer containing an iron-sulfur (Fexe2x80x94S) base, and a diffusion layer with an iron-nitrogen (Fexe2x80x94N) base is formed under the compound layer by nitridation, but the compound layer containing an iron-sulfur (Fexe2x80x94S) base coated on at least one side surface of the vane is removed.